A few-cycle high-energy fiber chirped pulse amplification system and method

Abstract

The application belongs to the field of femtosecond laser technology, and particularly relates to a few-cycle high-energy fiber chirped pulse amplification system and method. The system comprises a seed source module, a chirped pulse amplification module and a hybrid compression module. The seed source module adopts a nonlinear polarization rotation mode-locked resonator with an integrated tunable filter to generate linear chirped wide spectrum seed pulses with tunable central wavelength. The chirped pulse amplification module realizes energy amplification while effectively suppressing gain narrowing effect through a three-stage structure of pre-chirp management, pre-amplification and main amplification. The hybrid compression module adopts a cascaded scheme of a diffraction grating compressor and a fiber soliton self-compressor to finally compress the pulse width to two optical periods. The application solves the problem that high energy and few cycles are difficult to be considered in a C-band fiber amplification system, and can output high peak power pulses of hundreds of nanojoules and two optical periods.

Description

Technical Field

[0001] This invention belongs to the field of femtosecond laser technology, specifically relating to a short-period high-energy fiber chirped pulse amplification system and method. Background Technology

[0002] High-energy, few-period femtosecond lasers can output ultrashort pulses with extremely high instantaneous peak power, extremely wide spectral bandwidth, and extremely fast temporal resolution, playing an irreplaceable role in fields such as nonlinear optics, strong-field physics, attosecond science, optoelectronics, and biological imaging. Therefore, the development of few-period femtosecond lasers has significant scientific research and application value. The limitations of traditional fiber amplifiers in terms of output pulse energy and output pulse width restrict their application in high-energy output. The inherent physical requirements of high energy and short pulse width are mutually constraining, and their development is a history of continuously pushing physical limits and technological innovation.

[0003] Chirped pulse amplification (CPA) is a highly efficient, stable, and commercially viable ultrafast laser solution. However, current technologies attempting to generate short-period, high-energy erbium-doped fiber femtosecond lasers using an all-fiber structure still face a series of physical and technical bottlenecks. Regarding gain bandwidth and gain narrowing effects, short-period pulses require ultrawide bandwidth, but erbium-doped fiber has a relatively narrow intrinsic gain spectrum (approximately 30–50 nm), making it difficult to support broadband pulses with fewer than 5 periods. In terms of nonlinear effects, during high-energy amplification, the extremely high peak power causes any medium in the beam path (amplifying crystal, optical elements, even air) to exhibit strong nonlinear responses, such as self-phase modulation (SPM), self-focusing, and optical damage. These effects not only distort the wavefront and degrade beam quality but also introduce spectral distortion, severely limiting energy scaling capabilities. This was the most significant bottleneck in the development of high-intensity femtosecond lasers before the advent of CPA technology. Finally, regarding the extreme sensitivity of dispersion management, short-period pulses contain an extremely wide spectral composition. All optical materials introduce wavelength-dependent group delay dispersion (GDD) and higher-order dispersion (such as third-order dispersion TOD). Even materials with a thickness of micrometers or an air path of a few millimeters are sufficient to cause significant pulse broadening or complex time structures (leading pulses or trailing pulses). Therefore, achieving accurate dispersion measurement and compensation across octave bands is crucial for compressing pulses to the Fourier transform limit, placing extreme demands on the precision of devices such as chirped mirrors and acousto-optic programmable dispersion filters (AOPDF). However, using large mode area (LMA) fiber or hollow-core photonic crystal fiber increases system complexity and instability. Summary of the Invention

[0004] The purpose of this invention is to provide a short-period high-energy fiber chirped pulse amplification system and method to solve the problem that existing chirped pulse amplification technology is unable to simultaneously achieve high energy and short-period output in the C-band.

[0005] The present invention achieves the above objectives through the following technical solutions:

[0006] In a first aspect, the present invention proposes a short-period high-energy fiber chirped pulse amplification system, the system comprising a seed source module, a chirped pulse amplification module and a hybrid compression module connected in sequence by optical paths;

[0007] The seed source module includes a laser resonant cavity composed of a spatial optical path segment consisting of an optical fiber fusion splice segment and a cavity loss adjustment device, used to generate a broadband femtosecond seed pulse with linear positive chirp; the cavity loss adjustment device is used to adjust the loss within the resonant cavity to achieve tuning of the center wavelength of the seed pulse.

[0008] The chirped pulse amplification module includes a pre-chirped management unit, a pre-amplification stage, and a main amplification stage connected in sequence, used to perform dispersion control, time-domain broadening, and energy amplification on the seed pulse;

[0009] The hybrid compression module includes a cascaded diffraction grating compressor and a fiber optic soliton self-compressor. The diffraction grating compressor is used to compress the amplified pulse to the fs level, and the fiber optic soliton self-compressor generates soliton self-compression, obtaining a short-period pulse of two optical cycles through higher-order soliton evolution.

[0010] Furthermore, the fiber optic fusion splice segment includes a first pump source, a first wavelength division multiplexer, a first gain fiber, and a first collimator sequentially fused together via optical fibers; the spatial optical path segment includes a second collimator, a second quarter-wave plate, a first half-wave plate, an optical isolator, a polarization beam splitter, a cavity loss adjustment device, and a first quarter-wave plate sequentially arranged along the optical path; the first collimator and the first quarter-wave plate are optically connected to complete the conversion between the fiber path and the spatial optical path.

[0011] Furthermore, the cavity loss adjustment device is specifically a filter. By selecting filters with different optical density values, the resonant cavity loss is adjusted, thereby achieving tuning of the center wavelength of the output seed pulse in the range of 1550nm to 1610nm.

[0012] Furthermore, the optical density value of the filter is 1.3, which is used to adjust the center wavelength of the seed pulse to 1560nm.

[0013] Furthermore, the pre-chirped management unit is composed of dispersion-compensating fiber and single-mode fiber fusion spliced ​​together, and is used to introduce negative group velocity dispersion into the seed pulse to broaden the pulse;

[0014] The pre-amplification stage includes a first polarization-independent isolator, a second pump source, a second wavelength division multiplexer, and a second gain fiber connected in sequence by optical fibers, used for primary amplification of the pre-chirped pulse;

[0015] The chirped pulse amplification module also includes a time-domain stretching stage, which is composed of a section of dispersion-compensating fiber. Its input end is fused to the output end of the pre-amplification stage to reduce the peak power of the pulse after primary amplification.

[0016] Furthermore, the main amplification stage includes a second polarization-independent isolator, a third pump source, a beam combiner, a third gain fiber, and a third collimator;

[0017] The input terminal of the second polarization-independent isolator is fused to the output terminal of the time-domain stretching stage;

[0018] The signal input end of the beam combiner is fused to the output end of the second polarization-independent isolator, and the pump input end is connected to the third pump source via optical fiber.

[0019] The input end of the third gain fiber is fused to the output end of the combiner to amplify the power of the broadened pulse.

[0020] The input end of the third collimator is fused to the output end of the third gain fiber to convert the amplified pulse into a spatial optical path and output it to the hybrid compression module.

[0021] Furthermore, the diffraction grating compressor includes a second half-wave plate, a first transmission diffraction grating, a roof prism, a second transmission diffraction grating, and a right-angle prism arranged sequentially along the optical path;

[0022] The second half-wave plate is disposed in the output optical path of the chirped pulse amplification module to adjust the polarization state of the input pulse;

[0023] The ridge prism is positioned between the first transmission diffraction grating and the second transmission diffraction grating to allow the pulse to propagate back and forth between the grating pairs to form a four-way optical path, and to perform preliminary dispersion compensation on the pulse.

[0024] The right-angle prism is disposed in the reflected light path of the second transmission diffraction grating to change the direction of the light path and output a pre-compressed pulse.

[0025] Furthermore, the fiber-optic soliton self-compressor includes a fourth collimator and a compression fiber;

[0026] The input terminal of the fourth collimator receives pulses from the output of the right-angle prism;

[0027] The input end of the compressed optical fiber receives pulses from the output of the fourth collimator.

[0028] Furthermore, the compressed optical fiber is a single-mode optical fiber.

[0029] Secondly, the present invention proposes a method for pulse amplification using the pulse amplification system described above, the method comprising the following steps:

[0030] S1. Generate a broadband femtosecond seed pulse with adjustable center wavelength and linear positive chirp through the seed source module;

[0031] S2. Introduce negative group velocity dispersion into the seed pulse using the pre-chirp management unit;

[0032] S3. The pre-chirped pulse is amplified sequentially through the pre-amplification stage and the main amplification stage;

[0033] S4. The amplified pulse is stretched in the time domain using the time-domain stretching fiber.

[0034] S5. The broadened pulse is initially compressed using the diffraction grating compressor.

[0035] S6. The pre-compressed pulse is coupled into the fiber optic soliton self-compressor to generate a soliton self-compression effect. Through high-order soliton evolution, a femtosecond pulse of the order of 100 nanojoules and two optical cycles is output.

[0036] The beneficial effects of this invention are as follows:

[0037] This system employs a tunable filter in the seed source module for gain management, outputting a broadband linear chirped seed pulse with a tunable center wavelength. In the chirped pulse amplification module, pre-chirping management effectively suppresses gain narrowing during amplification, and the combination of pre-amplification and main amplification achieves efficient energy enhancement. Finally, by utilizing a cascaded diffraction grating compressor and a fiber soliton self-compressor in the hybrid compression module, the pulse width is compressed to two optical cycles. This system can output high-energy, short-cycle femtosecond pulses in the C-band at the level of hundreds of nanojoules, solving the problem of balancing high energy and short pulse width in traditional fiber amplification systems. Attached Figure Description

[0038] Figure 1 This is a system block diagram of a few-period high-energy fiber chirped pulse amplification system based on hybrid compression, as proposed in one embodiment of the present invention.

[0039] Figure 2 This is a schematic diagram of the internal device connections of a few-period high-energy fiber chirped pulse amplification system based on hybrid compression, according to an embodiment of the present invention.

[0040] Figure 3 This is a flowchart of a short-period high-energy fiber chirped pulse amplification method based on hybrid compression, as proposed in another embodiment of the present invention.

[0041] Figure 4 This is an example of the output spectrum of a self-similar mode-locked fiber laser in a specific embodiment of the present invention;

[0042] Figure 5 This is an example of a system output pulse diagram in a specific embodiment of the present invention.

[0043] Figures 1-2 In this structure, 1. First pump source; 2. First wavelength division multiplexer; 3. First gain fiber; 4. First collimator; 5. First quarter-wave plate; 6. Filter; 7. Polarizing beam splitter; 8. Optical isolator; 9. First half-wave plate; 10. Second quarter-wave plate; 11. Second collimator; 12. Mirror; 13. Pre-chirped; 14. First polarization-independent isolator; 15. Second pump source; 16. Second wavelength division multiplexer; 17. Second gain fiber; 18. Second polarization-independent isolator; 19. Dispersion-compensating fiber; 20. Third pump source; 21. Combiner; 22. Third... 23. Gain fiber; 24. Third collimator; 25. Second half-wave plate; 26. First transmission diffraction grating; 27. Second transmission diffraction grating; 28. Roof prism; 29. ​​Right-angle prism; 20. Fourth collimator; 100. Compressed fiber; 101. Seed source module; 102. Fiber fusion splice section; 203. Spatial optical path section; 200. Chirped pulse amplification module; 201. Pre-chirped management unit; 202. Pre-amplification stage; 203. Main amplification stage; 204. Time domain stretching stage; 300. Hybrid compression module; 301. Diffraction grating compressor; 302. Fiber soliton self-compressor. Detailed Implementation

[0044] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0045] The purpose of this application is to provide a short-period, high-energy fiber chirped pulse amplification system and method, solving the problem of obtaining high-energy ultrashort C-band pulses in chirped pulse amplification systems (C-band specifically refers to a commonly used wavelength band in optical communication, with a wavelength range of approximately 1530 nm to 1565 nm). It overcomes the gain narrowing effect limitation in high-energy femtosecond laser generation, achieving self-similar pulse evolution of the laser pulse within an erbium-doped fiber amplifier. The amplification process is accompanied by a broad spectrum, providing a new technical means to achieve high peak power pulses with hundreds of nanojoules and few optical periods. It should be noted that for femtosecond lasers, single-pulse energies of "hundreds of nanojoules (100 nJ)" and above can be considered high energy.

[0046] This application employs a mode-locked laser as the seed source for a chirped pulse amplification system. The seed source utilizes dispersion management and gain loss management, based on the passive mode-locking principle. By adding filters with different OD values ​​to adjust the cavity loss, a seed source with a tunable center wavelength is obtained. This allows for the output of high-beam-quality femtosecond pulsed lasers, which are easily self-starting, thus improving the stability of the fiber laser. The saturable absorber-like structure within the seed source laser, composed of a waveplate group and a spatial optical isolator, shortens the cavity length, meeting the requirements of high repetition frequency applications. Furthermore, it is highly integrated and cost-effective.

[0047] The fiber laser proposed in this application is based on the chirped pulse amplification principle and consists of a seed source, a time-domain stretching stage, a pre-amplification stage, a main amplification stage, and a compression stage. In the chirped pulse amplification system, pre-chirping is used during the pre-amplification and main amplification of the signal light, reducing gain narrowing during amplification. In the time-domain stretching stage, the dispersion value is optimized by adjusting the lengths of the dispersion compensation fiber and the single-mode fiber when further stretching the ultrashort pulse output from the fiber oscillator. To obtain high-energy, short-period femtosecond lasers, a hybrid soliton compression method is proposed. This involves initial compression via grating pairs, followed by a soliton self-compression process generated through the single-mode fiber for further compression. The hybrid soliton compressor designed in this application can generate short-period femtosecond lasers suitable for various application scenarios.

[0048] This solution can achieve the following:

[0049] 1. Obtain self-similar pulse seed sources with linear positive chirping and parabolic spectra using NPR passive mode-locking and dispersion management.

[0050] 2. By using filters with different OD values ​​to adjust the loss inside the resonant cavity, the center wavelength of the seed source spectrum is made to be around 1560nm.

[0051] 3. Use dispersion compensation devices to pre-chirp the pulses and adjust the dispersion to overcome the gain narrowing limitation during high-energy pulse amplification; use hybrid soliton compression technology, after initial compression by grating pairs, optimize the length of the single-mode fiber after the grating pairs to achieve soliton self-compression and obtain short-period pulses.

[0052] Example 1

[0053] Please combine Figure 1 and Figure 2 One specific embodiment of this application illustrates a short-period high-energy fiber chirped pulse amplification system, which includes a seed source module 100, a chirped pulse amplification module 200 and a hybrid compression module 300 connected in sequence by optical paths.

[0054] The seed source module 100 includes a laser resonant cavity composed of an optical fiber fusion splice section 101 and a spatial optical path section 102. The optical fiber fusion splice section 101 is constructed by fusion splicing single-mode fiber, dispersion-optimized fiber, and gain fiber to provide intracavity gain and perform dispersion management. The spatial optical path section 102 includes a waveplate group, an optical isolator, a polarization beam splitter prism, and a cavity loss adjustment device, which realizes nonlinear polarization rotation mode-locking and wavelength tuning functions through spatial optical path arrangement.

[0055] In this embodiment, specifically combined Figure 2 The seed source module 100 constitutes the core oscillator part of the system. The seed source module 100 adopts a hybrid cavity design, consisting of an optical fiber fusion splice section 101 and a spatial optical path section 102, forming a complete laser resonant cavity. The optical fiber fusion splice section 101 serves as the main gain and transmission component, including a first pump source 1, a first wavelength division multiplexer 2, a first gain fiber 3, and a first collimator 4, which are sequentially fused together by an optical fiber fusion splicer. The first pump source 1 can be a single-mode semiconductor laser diode with a center wavelength of 976 nm, fused to the pump port of the first wavelength division multiplexer 2 via a pigtail. The signal end of the first wavelength division multiplexer 2 uses OFS980-16 fiber, whose dispersion characteristics are superior to ordinary single-mode fiber, helping to achieve near-zero dispersion conditions at high repetition frequencies. The first gain fiber 3 is a positive dispersion erbium-doped fiber, providing both intracavity gain and compensating for intracavity negative dispersion. The first collimator 4 uses an FC / APC connector to collimate the fiber output light into a spatial beam.

[0056] Specifically, the spatial optical path segment 102 implements mode-locking and tuning functions, including a second collimator 11, a second quarter-wave plate 10, a first half-wave plate 9, an optical isolator 8, a polarizing beam splitter 7, a filter 6, and a first quarter-wave plate 5 arranged sequentially along the optical path. The output light of the first collimator 4 is precisely aligned with the optical path of the first quarter-wave plate 5, completing the conversion from fiber to space. The second collimator 11 recouples the spatial light into the optical fiber, forming a closed-loop resonant cavity. The waveplate group (5,9,10) and the polarizing beam splitter 7 together constitute a nonlinear polarization rotation mechanism to achieve passive mode-locking; the optical isolator 8 ensures unidirectional laser operation, prevents backlight damage, and assists in mode-locking self-starting; the filter 6 serves as a cavity loss adjustment device, adjusting the cavity loss by replacing filters with different optical density values ​​(OD values), thereby precisely tuning the center wavelength of the output seed pulse to the range of 1550nm to 1610nm.

[0057] As a preferred option, by selecting a filter with OD=1.3, the center wavelength can be stabilized at around 1560 nm, which matches the gain spectrum of erbium-doped fiber and optimizes the subsequent amplification efficiency.

[0058] In this embodiment, specifically combined Figure 2The chirped pulse amplification module 200 includes a pre-chirped management unit 201, a pre-amplification stage 202, and a main amplification stage 203 connected in sequence, used for dispersion control, time-domain broadening, and energy amplification of the seed pulse. A reflector 12 is provided between the chirped pulse amplification module 200 and the seed source module 100 for coupling the light output from the seed source into the amplification system.

[0059] Specifically, the pre-chirp management unit 201 is composed of a dispersion-compensating fiber 19 and a single-mode fiber spliced ​​together. This unit introduces negative group velocity dispersion into the linear positive chirped seed pulse from the seed source through the dispersion-compensating fiber 19, adjusting the overall chirp of the pulse. This pre-chirp treatment is a key step in suppressing the gain narrowing effect during subsequent amplification.

[0060] In one optional implementation, a pre-chirp unit 13 is provided in the chirped pulse amplification module 200. The main function of the pre-chirp unit 13 is to adjust the chirp amount of the seed source pulse. By reasonably adjusting the chirp amount, favorable conditions can be created for the subsequent amplification and compression processes of the system, thereby helping to obtain high-quality pulse output. Preferably, the pre-chirp unit 13 is constructed using dispersion-compensating fiber and single-mode fiber SMF-28 with optimized length, replacing traditional grating pairs or prism pairs. This design can not only effectively reduce the number of optical components in the system and reduce the complexity of the system, but also improve the stability of the system under different environmental conditions and make it easier to realize the integrated design of the system.

[0061] Specifically, the pre-amplification stage 202 performs primary amplification on the pre-chirped pulse. This stage includes a first polarization-independent isolator 14, a second pump source 15, a second wavelength division multiplexer 16, and a second gain fiber 17, which are sequentially spliced ​​together by optical fibers. The first polarization-independent isolator 14 prevents back-propagating light from damaging the preceding devices; the second pump source 15 can be a single-mode semiconductor laser diode with a center wavelength of 976 nm, and its pigtail is spliced ​​to the pump port of the second wavelength division multiplexer 16; the second gain fiber 17 is an erbium-doped fiber consistent with the seed source, and its length is optimized to compensate for splice loss and provide gain, increasing the pulse power to the level of hundreds of milliwatts.

[0062] The chirped pulse amplification module 200 also includes a time-domain stretching stage 204. This stage consists of a dispersion-compensating fiber 19, whose input end is fused to the output end of the pre-amplification stage 202, i.e., the output end of the second gain fiber 17. Its main function is to stretch the pulse after primary amplification to the picosecond level (approximately 48 ps) in the time domain, significantly reducing the peak power of the pulse and thus effectively suppressing the accumulation of nonlinear effects during the main amplification process.

[0063] Specifically, the main amplification stage 203 is responsible for power amplification of the time-domain stretched pulse. It includes a second polarization-independent isolator 18, a third pump source 20, a combiner 21, a third gain fiber 22, and a third collimator 23. The input end of the second polarization-independent isolator 18 is fused to the output end of the time-domain stretched stage 204 to continue providing optical path isolation protection. The combiner 21 is a (2+1)x1 type, with its signal input end fused to the output end of the second polarization-independent isolator 18, and its pump input end connected to the third pump source 20 via an optical fiber; the third pump source 20 uses a multimode fiber-coupled laser diode with a center wavelength of 976 nm. The input end of the third gain fiber 22 is fused to the output end of the combiner 21, and a large mode area fiber is selected. Finally, the amplified pulse is received and collimated by the third collimator 23, converted into a spatial optical path, and sent to the subsequent hybrid compression module 300.

[0064] In this embodiment, combined with Figure 2 The hybrid compression module 300 includes a cascaded diffraction grating compressor 301 and an optical fiber soliton self-compressor 302. The diffraction grating compressor 301 is used to compress the amplified pulse to the fs level, and the optical fiber soliton self-compressor 302 generates soliton self-compression, and obtains a few-period pulse of two optical cycles through high-order soliton evolution.

[0065] Specifically, the diffraction grating compressor 301 is responsible for the initial compression and dispersion compensation of the pulse. It includes a second half-wave plate 24, a first transmission diffraction grating 25, a roof prism 27, a second transmission diffraction grating 26, and a right-angle prism 28 arranged sequentially along the optical path. The second half-wave plate 24 is placed in the spatial optical path output from the chirped pulse amplification module 200 to precisely adjust the polarization state of the incident pulse, matching it with the polarization-sensitive direction of the subsequent grating to achieve the highest diffraction efficiency. The first transmission diffraction grating 25 and the second transmission diffraction grating 26 form a grating pair, and the roof prism 27 is placed between the two gratings, allowing the pulse to propagate back and forth within it, forming a four-way optical path structure. This design effectively increases the dispersion compensation optical path within a compact space, compensating for the negative group velocity dispersion introduced by the pulse and completing the initial compression. The right-angle prism 28 is placed in the reflection optical path of the second transmission diffraction grating 26 to change the direction of the optical path and guide the initially compressed pulse to the next stage.

[0066] Specifically, the fiber-optic soliton self-compressor 302 receives the incident initial compression pulse to generate soliton self-compression and achieve final pulse compression. It includes a fourth collimator 29 and a compression fiber 30. The input end of the fourth collimator 29 receives the spatial light pulse output from the right-angle prism 28 and efficiently couples it into the fiber. The input end of the compression fiber 30 is connected to the output end of the fourth collimator 29 via fiber fusion splicing; this fiber is preferably a section of optimized-length single-mode fiber, such as 17cm of SMF-28. As the pulse propagates in the fiber, it generates a soliton self-compression effect. This process enables a pulse width output of sub-two optical cycles, with pulse energy reaching the sub-100 nanojoule level.

[0067] In one specific implementation of the present invention, the system is constructed by sequentially connecting the following three parts via optical paths: First, a broadband self-similar mode-locked fiber laser serves as the seed source of the system, used to generate a broadband femtosecond seed pulse with tunable center wavelength and linear positive chirp characteristics; then, an all-fiber chirped pulse amplifier performs dispersion modulation, time-domain broadening, and multi-stage energy amplification on the seed pulse; finally, a hybrid soliton compressor performs dispersion compensation and pulse compression on the amplified pulse, first performing initial compression through a diffraction grating, and then further generating higher-order soliton evolution through the soliton self-compression effect in the fiber, ultimately outputting a high-energy, short-period femtosecond pulse. In this implementation, the system uses an all-fiber structure as the main body, combined with spatial optical path compression design, taking into account the system's integration, stability, and high-performance output.

[0068] Example 2

[0069] Please combine Figure 3 This embodiment proposes a method for pulse amplification using the pulse amplification system as described in Embodiment 1, the method comprising the following steps:

[0070] S1. A broadband femtosecond seed pulse with tunable center wavelength and linear positive chirp is generated through the seed source module 100. This step precisely tunes the center wavelength of the output seed pulse to the range of 1550 nm to 1610 nm, preferably around 1560 nm, by adjusting the loss of the cavity loss adjustment device in the resonant cavity (such as replacing filters with different OD values), to match the gain spectrum of the subsequent erbium fiber amplifier. The seed pulse has an approximately parabolic spectrum and linear positive chirp characteristics.

[0071] S2. Introduce negative group velocity dispersion into the seed pulse using the pre-chirp management unit 201. This step partially compensates for the inherent linear positive chirp of the seed pulse by combining a section of dispersion-compensating fiber of a specific length with a single-mode fiber, thus adjusting the overall chirp amount. This pre-chirp processing is a crucial pre-processing step to suppress spectral narrowing caused by gain narrowing during subsequent amplification.

[0072] S3. The pre-chirped pulse is sequentially amplified through a pre-amplification stage 202 and a main amplification stage 203. The pre-amplification stage uses a single-mode pump source (such as a 976 nm laser diode) and a section of erbium-doped fiber to initially amplify the pulse power to the level of hundreds of milliwatts. The main amplification stage uses a multimode high-power pump source (such as a 27 W multimode laser diode) and a large mode area erbium-ytterbium co-doped fiber. The pump light is coupled to the signal light through a combiner to further amplify the power, and the final output average power can reach the level of watts (approximately 5 W).

[0073] S4. The amplified pulse is broadened in the time domain using a time-domain broadening stage 204 (composed of dispersion-compensating fiber 19). This step further broadens the picosecond-level chirped pulse to tens of picoseconds (e.g., about 40 ps), significantly reducing its peak power and thus effectively suppressing nonlinear effects (such as self-phase modulation and self-focusing) that may occur during the main amplification process, providing a guarantee for safe high-energy amplification.

[0074] S5. The broadened pulse is initially compressed and its dispersion compensated using a diffraction grating compressor 301. This step utilizes a four-way optical path structure composed of a transmission diffraction grating and a roof prism to compensate for most of the group velocity dispersion (GDD) introduced by the pulse, thereby achieving initial pulse compression and reducing the pulse width to the order of hundreds of femtoseconds.

[0075] S6. The pre-compressed pulse is coupled into the fiber-optic soliton self-compressor 302. This step first uses a collimator to efficiently couple the spatial light pulse into the fiber path, and the pulse then propagates in the fiber (such as a single-mode fiber or a cascade of a single-mode fiber and a highly nonlinear fiber). By carefully optimizing the length and dispersion characteristics of the two-stage fiber, and utilizing the soliton self-compression effect and higher-order soliton evolution during pulse propagation, a high-quality femtosecond pulse with a pulse width sub-two optical cycles (corresponding to a center wavelength of 1560nm, approximately sub-15 fs) and a single-pulse energy on the order of hundreds of nanojoules is finally output.

[0076] To more clearly illustrate the present invention and its advantages, the following will further explain the system and method provided by the present invention in conjunction with specific implementation examples and related partial figures.

[0077] This case study constructs a self-similar mode-locked fiber laser as the seed source. Three types of fiber are used: OFS980-16, SMF-28, and EDF OFS80. Dispersion management is achieved through precise fiber length recutting, resulting in a parabolic broadband spectrum. Inside the laser cavity, an optical density (OD) filter of 1.3 is used as a cavity loss adjustment device for gain management, precisely adjusting and stabilizing the center wavelength of the output spectrum. It should be noted that the cavity loss adjustment device is not limited to a specific filter; optical attenuators, adjustable beam splitters, or other optical devices capable of flexibly adjusting intracavity loss can also be used to achieve tuning of the seed pulse center wavelength within a specific range.

[0078] exist Figure 4 In the graph, the horizontal axis represents wavelength, measured in nanometers (nm), with the wavelength range set between 1480nm and 1640nm. The vertical axis represents intensity, measured in dBm. Figure 4 The displayed curve showing the change in light intensity with wavelength clearly shows that the light intensity reaches its peak at the center wavelength of 1566.73 nm, while also providing a direct 3dB width of 40.92 nm. Combined with... Figure 4 The final output results show that the self-similar mode-locked fiber laser seed source achieved stable mode-locked pulse output. Its output power is 1mW, the spectral width reaches 40nm, the center wavelength is precisely located at 1566nm, and the repetition rate is 33MHz.

[0079] The signal light output from the polarization beam splitter is coupled into the optical fiber. The pre-chirped stage, composed of dispersion-compensating fiber and single-mode fiber, provides a certain amount of negative chirp to alleviate the gain narrowing phenomenon that occurs during subsequent amplification. It should be understood that the structure of the pre-chirped management unit is not limited to this; it can also be implemented using dispersion-tunable devices such as transmission or reflection diffraction grating pairs or prism pairs to provide flexible and adjustable chirp management capabilities. The pre-chirped light enters the wavelength division multiplexer, pumped by a 976nm single-mode diode laser, boosting the power to the hundreds of milliwatts level. The pre-amplified light enters the polarization-independent isolator to prevent backlighting from damaging the pre-amplifier. The signal light output is fused with the dispersion-compensating fiber, stretching it to approximately 40ps in the time domain, significantly reducing the peak power and nonlinear accumulation of the subsequent amplification stage, creating conditions for the subsequent main amplification.

[0080] The output light is connected to a beam combiner and pumped by a 27W multimode pump source laser. The multimode output fiber of the 27W fiber-coupled LD is connected to the pump end of the fiber combiner. The output end of the combiner is welded with a 10μm core diameter, 125μm cladding double-clad erbium-ytterbium co-doped fiber, with a fiber length of 2.9m. This stage achieves an output amplification power of 5W. The amplified light passes through a half-wave plate to adjust the polarization state of the light to achieve the maximum diffraction efficiency of the grating pair. After being collimated, the output light is compressed, with a compression efficiency typically between 80% and 85%.

[0081] The amplified signal light undergoes initial compression via a transmission diffraction grating. By incorporating a roof prism to form a double-pass structure, the pulse travels back and forth through the grating pair, undergoing four diffractions to effectively compensate for the introduced positive dispersion. The initially compressed pulse is then output via a right-angle prism and coupled into a fiber-optic soliton self-compressor. This compressor consists of a fourth collimator and a compression fiber (17 cm single-mode fiber). Through the soliton self-compression effect, it generates a higher-order soliton, which evolves to produce a few-period pulse. It is understood that the fiber combination used to achieve soliton self-compression is not limited to the specific type and length mentioned above; other fiber combinations optimized for dispersion and nonlinearity, such as a combination of single-mode fiber and dispersion-compensating fiber, can also be used to achieve the best compression effect. After this nonlinear compression, the pulse ultimately outputs a high-peak power pulse on the order of hundreds of nanojoules, spanning two optical cycles.

[0082] like Figure 5 As shown, the horizontal axis represents the delay time (Delay), measured in picoseconds (ps), ranging from -1ps to 1ps; the blue curve on the vertical axis represents intensity, reflecting the pulse energy distribution and showing the intensity changes after amplification and compression; the orange curve represents phase (rad), showing the change of pulse phase over time and allowing for the evaluation of effects such as dispersion compensation; the final output pulse has a time domain width of 12.8 fs, a symmetrical intensity distribution, and a flat phase, indicating that the evolution of higher-order solitons has generated a high-quality few-period pulse.

[0083] Through the above implementation methods, this invention successfully achieves the goal of outputting high-energy, short-period femtosecond pulses in the C-band. By organically combining gain and dispersion management, pre-chirp processing, and hybrid compression techniques, the system effectively suppresses gain narrowing and nonlinear effects, ultimately achieving a pulse width of less than 12.8 fs (centered at 1560 nm) and a single-pulse energy reaching the hundred nanojoule level.

[0084] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A few-cycle high-energy fiber chirped pulse amplification system, characterized in that, The system comprises a seed source module (100), a chirped pulse amplification module (200) and a hybrid compression module (300) connected in sequence by optical paths; The seed source module (100) comprises a laser resonant cavity composed of a fiber fusion section (101) and a spatial light path section (102) of a cavity loss adjusting device, for generating a wide spectrum femtosecond seed pulse with linear positive chirp; the cavity loss adjusting device is used for adjusting the loss in the resonant cavity to achieve the tuning of the center wavelength of the seed pulse; the cavity loss adjusting device is specifically a filter (6), by selecting the filter (6) with different optical density values to adjust the loss of the resonant cavity, thereby achieving the tuning of the center wavelength of the output seed pulse in the range of 1550nm to 1610nm; The chirped pulse amplification module (200) comprises a pre-chirp management unit (201), a pre-amplification stage (202) and a main amplification stage (203) connected in sequence, for dispersion regulation, time domain expansion and energy amplification of the seed pulse; The hybrid compression module (300) comprises a cascaded diffraction grating compressor (301) and a fiber type soliton self-compressor (302), the diffraction grating compressor (301) is used for compressing the amplified pulse to the order of fs, and the soliton self-compression is generated in the fiber type soliton self-compressor (302), and two optical period short period pulses are obtained through high order soliton evolution; The pre-chirp management unit (201) is composed of a dispersion compensation fiber and a single mode fiber fusion, for introducing negative group velocity dispersion to the seed pulse for pulse expansion; The pre-amplification stage (202) comprises a first polarization independent isolator (14), a second pump source (15), a second wavelength division multiplexer (16) and a second gain fiber (17) connected by optical fibers in sequence, for primary amplification of the pre-chirp processed pulse; The chirped pulse amplification module (200) further comprises a time domain expansion stage (204) composed of a dispersion compensation fiber (19), the input end of which is fused with the output end of the pre-amplification stage (202), for reducing the peak power of the pulse after primary amplification; The main amplification stage (203) comprises a second polarization independent isolator (18), a third pump source (20), a beam combiner (21), a third gain fiber (22) and a third collimator (23); The input end of the second polarization independent isolator (18) is fused with the output end of the time domain expansion stage (204); The signal input end of the beam combiner (21) is fused with the output end of the second polarization independent isolator (18), and the pump input end is connected with the third pump source (20) through an optical fiber; The input end of the third gain fiber (22) is fused with the output end of the beam combiner (21), for power amplification of the expanded pulse; The input end of the third collimator (23) is fused with the output end of the third gain fiber (22), for converting the amplified pulse into spatial light path and outputting to the hybrid compression module (300); The diffraction grating compressor (301) comprises a second half-wave plate (24), a first transmissive diffraction grating (25), a roof prism (27), a second transmissive diffraction grating (26) and a right-angle prism (28) arranged in sequence along an optical path; The second half-wave plate (24) is arranged in an output optical path of the chirped pulse amplification module (200) and used for adjusting a polarization state of an input pulse; The roof prism (27) is arranged between the first transmissive diffraction grating (25) and the second transmissive diffraction grating (26) and used for making the pulse propagate back and forth between grating pairs to form a four-pass optical path and preliminarily compensate the pulse for dispersion; The right-angle prism (28) is arranged in a reflection optical path of the second transmissive diffraction grating (26) and used for changing an optical path direction and outputting a preliminarily compressed pulse.

2. The few-cycle high-energy fiber-chirped pulse amplification system according to claim 1, wherein, The optical fiber fusion section (101) comprises a first pump source (1), a first wavelength division multiplexer (2), a first gain optical fiber (3) and a first collimator (4) fused by optical fibers in sequence; the spatial optical path section (102) comprises a second collimator (11), a second quarter-wave plate (10), a first half-wave plate (9), an optical isolator (8), a polarization beam splitter prism (7), a cavity loss adjusting device and a first quarter-wave plate (5) arranged in sequence along an optical path; the first collimator (4) is optically connected with the first quarter-wave plate (5) to complete conversion of an optical fiber path and a spatial optical path.

3. A few-cycle high-energy fiber chirped pulse amplification system according to claim 2, characterized in that, The optical density value of the filter (6) is 1.3 and used for adjusting the center wavelength of the seed pulse to 1560 nm.

4. The few-cycle high-energy fiber-chirped pulse amplification system of claim 1, wherein, The optical fiber type soliton self-compressor (302) comprises a fourth collimator (29) and a compression optical fiber (30); The input end of the fourth collimator (29) receives the pulse output from the right-angle prism (28); The input end of the compression optical fiber (30) receives the pulse output from the fourth collimator (29).

5. A few-cycle high-energy fiber-chirped pulse amplification system according to claim 4, characterized in that, The compression optical fiber (30) is a single-mode optical fiber.

6. A method of pulse amplification using the pulse amplification system according to any one of claims 1 to 5, characterized by, The method comprises the following steps: S1, generating a wide-spectrum femtosecond seed pulse with adjustable center wavelength and linear positive chirp by the seed source module (100); S2, introducing negative group velocity dispersion to the seed pulse by the pre-chirp management unit (201); S3, amplifying the pulse subjected to pre-chirp processing by the pre-amplification stage (202) and the main amplification stage (203) in sequence; S4, expanding the amplified pulse in time domain by the time-domain expansion optical fiber (19); S5, preliminarily compressing the expanded pulse by the diffraction grating compressor (301); S6, coupling the preliminarily compressed pulse into the optical fiber type soliton self-compressor (302) to generate a soliton self-compression effect and output a femtosecond pulse with a hundred nanjoule level and two optical periods via high-order soliton evolution.

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